1. Field of the Invention
The present invention relates to electrical connector assemblies such as those used to connect portions of electrical utilities, and more particularly, to loadbreak separable connectors.
2. Description of the Related Art
High-voltage separable connectors interconnect sources of energy, such as transformers, to distribution networks and the like. Frequently, it is necessary to connect and disconnect the electrical connectors. These connectors typically feature a male connector which contains a male contact, and a female connector which contains a female contact. The male connector may be in the form of an elbow connector or a protective cap, for example, and the female connector may be in the form of a bushing. The male contact is typically maintained within the elbow connector or protective cap, and the female contact is contained within the bushing.
Disconnecting energized connectors is an operation known as loadbreak. During loadbreak, the male connector (e.g., elbow connector or protective cap) is pulled from the female connector (e.g., bushing) using a hotstick to separate the connectors. This, in effect, creates an open circuit. During loadbreak, a phenomenon known as a flashover may occur, whereby an arc from an energized connector extends rapidly to a nearby ground. Existing connector designs contain a number of arc extinguishing components so that the connectors can have loadbreak operations performed under energized conditions with no flashover to ground occurring. Even with these precautions, however, flashovers have occurred on occasion.
A breakdown in dielectric strength of the air surrounding the metal contacts can occur before the metal contacts that carry the load current actually separate. This breakdown may result in a small flash which causes little or no damage, but which may cause contamination of the interface between the male connector and female connector. On rare occasions, the flash is accompanied by a power follow current that can cause a large external arc. A large external arc may damage the equipment or possibly create a power outage.
The reduction in dielectric strength arises because the dielectric strength of air is a function of pressure. When the connectors are being disconnected, a partial vacuum is created by the expansion of the volume of the enclosed space between the male connector and the female connector. The increased volume during this initial separation results in a lower air pressure and reduced dielectric strength of the air surrounding the energized portions of the connectors.
The reduction in dielectric strength may be especially pronounced in cold weather, for example, or where the lubricating grease between the connectors has evaporated or has been forced out of the interface between the male connector and the female connector. Without sufficient lubrication, the elbow connector or protective cap grabs the bushing tightly, causing the elbow or cap to stretch to a significant extent before separating. This further expands the cavity between the elbow or cap and bushing, resulting in a significant reduction in pressure and dielectric strength, which increases the likelihood of a flashover.
The reduction in air pressure during disconnection also increases the force required to separate the male connector from the female connector, as the suction tends to increase the force which holds the parts together. Conversely, the surrounding air must be compressed during insertion of the male connector onto the female connector, which increases the force necessary to connect the two parts.